Conventional lithium-ion secondary batteries use a liquid electrolyte solution, which mainly comprises an organic solvent and a lithium salt. When such a lithium-ion secondary battery operates at a high rate, leakage of the electrolyte solution or even combustion or explosion of the battery is likely to happen because of the high operating temperature.
The solid-state polymer electrolyte is a kind of solid electrolyte material that has experienced rapid development in recent years. Because the solid-state polymer electrolyte comprises no liquid organic solvent, the shortcomings that the battery is prone to liquid leakage and that combustion and explosion may be caused when the operating temperature is too high are overcome. According to some researches, the solid-state polymer electrolyte can further effectively suppress growth of lithium dendrites in the charging process, thereby eliminating the risk of internal short-circuit faults that may be caused due to growth of the lithium dendrites. Furthermore, the solid electrolyte has the functions of both an electrolyte solution and a separator, and this eliminates the need of using the separator and also eliminates the need of protection which would be required by a liquid-electrolyte battery in an overcharged state. Therefore, this makes the battery relatively easier to be manufactured. The polymer electrolyte has advantages such as a light weight, good tenacity and good flexibility and is easy to be formed into a thin film, so it can further increase the energy density of the lithium-ion secondary battery.
The solid-state polymer electrolytes that have been developed may be mainly classified into all solid polymer electrolytes and gel polymer electrolytes. The existing all solid electrolytes are mainly solid materials formed by lithium salts (e.g., LiClO4, LiBF4, LiAsF6, LiPF6 etc.) dissolved in polyester (e.g., PEO or PPO) or polyether having a high molecular weight; and the gel polymer electrolytes are usually formed by adding a liquid plasticizer and/or a solvent into a polymer matrix to form a stable gel structure. However, no polymer electrolyte having a relatively high ionic conductivity within a relatively wide temperature range has been found yet, so increasing the conductivity of the polymer electrolyte at the room temperature has become a hot topic of research on the solid-state polymer electrolyte.